Keying



Nov. 17, 1936. C. w. HANsx-:LL

KEYING Filed May 24, 1935 INVENTOR keyed in accordance with the presentinvention for the grid electrodes of the vacuum tubes is Patented Nov.17, 1936 UNETED STATES PATENT GFFICE KEYING Clarence W. Hansell, Port`lefferson, N. Y., assignor to Radio Corporation of America, acorporation of Delaware Application May 24, 1933, Serial No. 672,529 lClaim. (Cl. Z50-17) v The present invention relates to signallingsyscillation generator as described above form no tems and more inparticular to a novel method part of the present invention and may be asdisof and means for modulating or keying high freclosed or may be of anytype known.

quency oscillations. The oscillations may be In the circuit shownnegative bias potential in the circuit in which they are produced or insupplied by way of a direct current circuit comamplifying stages orrepeating stages between the pleted between the grids and cathodes ofsaid point of production and the point of utilization. tubes by way ofthe resistor R. The value of The novel features of my invention havebeen said resistance is such as to normally bias said pointed out withparticularity in the claim aptubes to a point at which they produceoscilla- 10l pended hereto. tions most efciently. The transmitter ismod- My method of modulating or keying high freulated or keyed byimposing on the oscillator quency oscillations and the means wherebysaid grids variations in negative potential from the method may becarried out will be understood keying circuit at the right of theoscillator, which from the detailed description which follows and willnow be described as it is used to interrupt 3 therefrom when read inconnection with the said oscillations for telegraph keying. drawing, inwhich the single figure illustrates The modulating or keying circuitshown comschematically a signalling means including oscilprises a pairof rectifiers V1 and V2 connected as lation producing or relaying meansand an arshown in a full wave rectifier circuit. This is rangement formodulating or keying the oscillaaccomplished by connecting the anodes oftubes V2@ tions produced or relayed in accordance with my V1 and V2 inpush-pull relation with the se-cinvention. ondary Winding of atransformer T1, the pri- In the circuit shown it is assumed thatoscilmary winding of which is connected to a source lations are to be.produced and keyed in the proof alternating current. The cathodes oftubes ducing means, although, as indicated above, it V1 and V2 may besupplied with lament heating 25 Will be lll'ldSIStOOd that themodulating OI keying Current from any Source, as, for example, the meansof the present invention may be associated source connected with thetransfo-rmer T1 by way with stages subsequent to the point of producoftransformers TF1. The electrical center of tion of the oscillations. Inthe drawing I have the secondary winding of transformer T1 is con- 30shown an oscillator O comprising a pair of thernected by way of areactance XL to the terminal 30 mionic tubes having their outputelectrodes conof the resistance R as shown. The electrical cennected asshown by Way of a tank circuit 2 couters of the secondary windings oftransformers pled to a load circuit. The load circuit may be TF1 areconnected as shown to the anodes of a an antenna system A, or it may bethe input to pair of keying tubes V3 and V4. The cathodes an amplifier.The control grids of the oscillators of the tubes V3 and V4 may beconnected with 35 are likewise coupled by way of a tuned circuit 4 thesecondary windings of transformers TF2, the including an inductance.Tuned circuit t may primary windings of which may be connected be tunedto the fundamental frequency, while with the common alternating currentsource or tuned circuit 2 may be tuned substantially to the with anyother source. having its voltage prop- 40 fundamental frequency or, ifthe tubes are used erly adjusted. The electrical centers of the sec- 40as frequency multipliers having control energy ondary windings of thetransformers TF2 are input from a previous stage, the output tunedconnected as shown to ground to one terminal circuit 2 may be tuned to aharmonic of the of the resistance R1 and to the positive terminalfundamental frequency. When the tubes are of the source B. The otherterminal of resistance used as oscillators in the circuit shown the pro-R1 is connected by way of resistances R2 and R3 45 duction ofoscillations may b-e insured by interto the control grids of tubes V3and V4 as shown. connecting the anodes and control grids of the Thesource B may be connected in parallel with tubes by way of variablecapacities as shown. Pothe resistance R1 by way of key or relay K, astential for the anode circuits of the tubes is supshown. The key K maybe manually operated plied by way of an inductance L connected as oractuated by way of a relay which is in turn 50 shown to the positivelterminal of any suitable controlled by currents over a wire line from asource, such as a battery, rectifier, or generator, remote point. Thealternating currents imthe negative terminal of which is connected topressed on transformer T1 are rectified in the ground, tubes V1, V2 andfiltered by the action of the n- The frequency determining circuits ofthe osductance XL and the parallel capacity C. The 55 direct currentpath of the rectifier includes as shown the resistance R and theinternal impedances of the tubes V3 and V4 in series. The internalimpedances of the tubes V3 and V4 are Variable and may be varied bymanipulating the key or relay K.

In operation when the key or relay K is in the lower position, that is,in the position to connect the source B in parallel with the resistanceR1, the negative potential applied from the source B to the grids oftubes V3 and V4 biases said grids negatively to a point at which tubesV3 and V4 become non-conductive or are cut 01T. The impedances of thesetubes are in series with the rectiiier including the tubes V1, V2 andsaid rectiiier, for this reason, is rendered inoperative so that nonegative potential is supplied by the keying circuits to the grids ofthe oscillators in O. The bias on the grids of the oscillators O is atthis time determined by the direct current flowing in the grid cathodecircuit of the oscillators due to grid rectication. The elements of thegrid circuit of the oscillators O are so chosen that the potential onsaid grids is such as to produce sustained oscillations of constantamplitude and good energy eiciency in said tubes. When key or relay K ismoved into an upper position, that is, removes the source B from thegrid circuit, the potential on the grids of tubes V3, V4 becomes Zero orless negative and said tubes become conductive. This permits directcurrent from the rectiiier tubes V1, V2 to iiow in the series circuitincluding the impedance of tubes V3, V4 and the resistance R. Thisimpresses a high negative potential on the control grids of the tubes inthe oscillators O and biases said tubes to cut oif so that said tubes nolonger produce oscillations.

Obviously, I may adjust the potential from source B to such a value thatpartial current flows through the tubes V3, V4, the bias rectiiier andthe resistance A. Then, by introducing modulating energy in series withsource B, for example, by means of a transformer, I may use the systemfor telephony or modulated telegraphy.

Although my keying system has been shown as applicable to an oscillationgenerator, it will be understood that I do not intend to limit my keyingand modulating circuit to such use since, obviously, the stage O may bean oscillation repeating stage rather than an oscillation producingstage. When oscillations are repeated in stage O rather than producedtherein, the same keying results may be obtained by connecting my keyingcircuit with the grid circuit of the repeater stage in the same mannerin which it is connected to the oscillator stage used for purposes ofillustration.

An outstanding advantage of my keying and modulating system is that thecathodes of tubes V3 and V4 and one end of their input circuit may be atground potential. This greatly reduces the amount of insulation requiredin the input circuit and removes serious limitations to the keyingspeeds readily obtainable when the transmitter is controlled over a Wireline.

Another outstanding advantage when the system is used for ordinarytelegraphy is that the stage O is rendered inoperative while currentiiows from the bias source through the keying or modulating tubes V3,V4. Therefore, fluctuations or ripples in the output of the bias sourceor in the input control potential to tubes V3, V4 have no effect uponthe output from stage O so long as the potential across resistance R ishigh enough to prevent iiow of current in tubes of stage O. When stage Ois rendered operative no current ows through resistance R from the biassource and the keying circuits, therefore, can not introduce undesiredmodulation in the output of stage O.

Having thus described my invention and the operation thereof, what Iclaim is:

A signalling device comprising, a pair of thermionic tubes having theircontrol grids connected by an alternating current circuit including anindu-stance, a resistance connected between the electrical center ofsaid inductance and the cath- @des of said tubes, said resistance beingof such a value that the potential on the control grid of said tubes dueto grid rectification of alternating currents in said alternatingcurrent circuits permits said tube to repeat or amplify said alternatingcurrent, and means for altering the operativeness of said tube at signalfrequency comprising, a direct current path in parallel with saidresistance, said path including a pair of rectiers having their anodesconnected to the electrical center of said inductance and their cathodesconnected to the anodes of a pair of modulating tubes, the cathodes ofwhich modulating tubes are connected to the cathodes of said iirst namedtubes and a source of modulating potentials connected between the'control grid and cathodes of said modulating tubes.

CLARENCE W. HANSELL.

